This invention relates to idling control apparatus for internal combustion engines, and more particularly it is concerned with an idling control apparatus for an internal combustion engine wherein air for sustaining idle running of the engine that bypasses the throttle valve mounted in the suction conduit in the throttle body has its quantity controlled in accordance with changes in the temperature of the engine.
Generally, an internal combustion engine has a throttle valve mounted in the section conduit for controlling the quantity of air supplied to the engine as the driver of the vehicle operates the throttle valve, regardless of whether the engine is of the fuel injection type or the carburetor type. In an internal combustion engine, an idling control apparatus is mounted separately from the throttle valve for controlling the quantity of air supplied to the engine during idle running thereof. The idling control apparatus is designed to effect control of idle running of the engine by means of a valve mounted in a passage for air for idle running of the engine which communicates a portion of the suction conduit upstream of the throttle valve with a portion of the suction conduit downstream of the throttle valve by bypassing the throttle valve, for controlling the quantity of air flowing through such passage in accordance with changes in the temperature of the engine.
One example of idling control apparatus disclosed in U.S. Pat. No. 3,645,509 comprises a valve element mounted in a passage bypassing the throttle valve which is operated by means of a heat sensitive, expanding body in a fluid state.
The use of a heat sensitive, expanding body in a fluid state for operating a valve element of an idling control apparatus as disclosed in U.S. Pat. No. 3,645,509 requires the provision of means for providing a liquidtight seal specifically fitted for this purpose. When the heat sensitive, expanding body in a fluid state undergoes deterioration with the passage of time, the quantity of air flowing through the passage by bypassing the throttle valve would vary from the quantity of air that flows through the passage when the apparatus is initially fitted to the internal combustion engine. Particularly, the heat sensitive, expanding body in a fluid state is faced with a difficulty in keeping its initial characteristics over a prolonged period of time. Moreover, a large number of part that are required for this type of idling control apparatus makes its cost high. In view of these problems, this type of idling control apparatus would not readily be put into practical use.
Meanwhile proposals have been made to use, in place of a heat sensitive, expanding body in a fluid state described in U.S. Pat. No. 3,645,509, a bimetal member in the form of a spiral substantially similar to the choke mechanism disclosed in U.S. Pat. No. 3,898,967, in an idling control apparatus for an internal combustion engine.
The butterfly valve operated by the bimetal member described in U.S. Pat. No. 3,898,967 is a choke valve which is opened with the progress of operation of the engine. On the other hand, in an idling control apparatus, a valve operated by a bimetal member should be closed with the progress of operation of the engine.
The idling control apparatus using a bimetal member is substantially similar to the apparatus disclosed in U.S. Pat. No. 3,898,967 except that the operation of the butterfly valve is reversed. More specifically, the idling control apparatus using a bimetal member comprises a butterfly valve located in a passage for air for idle running of the engine which communicates a portion of the suction conduit upstream of the throttle valve with a portion of the suction conduit downstream of the throttle valve by bypassing the throttle valve, the butterfly valve being supported for rotation by a shaft having secured thereto a lever which is in engagement with the end of an outermost convolution of the spiral bimetal member (movable end), and a pin secured to a bimetal housing for fixedly supporting the end of an innermost convolution of the spiral bimetal member (fixed end). As the temperature of the engine rises, the butterfly valve reduces the area of the passage for air for sustaining idle running of the engine.
The aforesaid idling control apparatus using a bimetal member offers the advantages of being simple in construction and low in cost. However, one of the problems encountered with regard to this apparatus is flapping of the butterfly valve which occurs during idle running of the engine and causes variations to occur in the quantity of air flowing through the passage for air for idle running of the engine.
This problem arises primarily from vibration of the bimetal member. More specifically, in an idling control apparatus using a bimetal member, the end of an innermost convolution of the bimetal member is a fixed end and the end of an outermost convolution thereof is a movable end, so that the bimetal member itself functions as a spring. Particularly, vibration of the engine causes the end of the outermost convolution of the spiral bimetal member to vibrate, thereby causing flapping of the butterfly valve to take place. Vibration of the bimetal member is transmitted from the end of the outermost convolution of the bimetal member which is a movable end to the shaft and lever, and vibration of the bimetal member tends to increase or reduce the opening of the butterfly valve, thereby varying the quantity of air flowing through the valve.
In addition, the butterfly valve itself is concerned in the development of variations in its opening. Like a known choke valve of a carburetor, the butterfly valve is supported by a shaft in a position which is eccentric and not at the center of the surface of the valve. Thus pulsation of the sucked air which occurs with the operation of the engine would cause the butterfly valve to vibrate, thereby adding to the vibration of the butterfly valve caused by the vibration of the bimetal member as aforesaid.
For the reasons stated hereinabove, the air flowing through the passage for air for idle running of the engine of an idling control apparatus of the prior art has tended to show variations during operation of the engine, thereby making it impossible to obtain stable idle running of the engine.
As described hereinabove, idling control apparatus can be broadly classified into two groups: one group using a heat sensitive, expanding body in a fluid state and the other group using a metallic heat sensitive, expanding body, such as a bimetal member.
This invention is directed to an idling control apparatus for an internal combustion engine using a bimetal member, which is relatively simple in construction and low in cost.